Fueling Insanity. The drop "Spine Crusher" is one of the drops, from Undead Giant. People had problems getting it because of low drop rate.

People have also posted screenshots on Alina's twitter, telling her that there is no bug, that they "fixed it"

Or it's glitched, meaning that for some people it works, for some it dosen't. Maybe they havent even added the item to Undead Giant yet, and with the people telling them it's alright, they havent tried too hard.